You are a failure of human.
You are a failure of a human.
Well, first, is putting 'a' in there grammatical? If so, what's the difference from when there's no 'a' there?
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You are a [nounA] of a [nounB].
This is a very common way of saying things, where nounA is often things like failure or similar. It means:
As a [nounB], you are a [nounA].
In this case,
As a human, you are a failure.
You are a failure at being a human. It's a pretty weird thing to say.
You need the article because human is a singular countable noun here, so it needs some sort of determiner. If human is an adjective, as it sometimes is, obviously it doesn't need a determiner - but there's no way it can be an adjective here.